The invention concerns a method and an apparatus for protecting an injection device in a blast furnace. Specifically, the invention is directed to a method and apparatus for cooling the injection lance disposed in the hot blast conduit.
Injection lances for injection coal dust as a substitute fuel, for example for piece coke and heating oil, into the hot blast conduit of a blast furnace by means of a carrier gas, have long been used in the smelting of iron ores (Stahl und Eisen 110, 1990, pages 35-40). In recent times endeavours have been made to increase the maximum amounts of coal dust which hitherto could be injected by the injection of oxygen or an oxygen-bearing gas together with the coal dust which is entrained by a carrier gas.
In conjunction with the hot blast temperature which is about 1200.degree. C., that results in a strong tendency to burn back in the mouth region of the injection lance.
U.S. Pat. No. 3,758,090 discloses an arrangement with which an injection lance for injecting fuel, which is fitted into the hot blast conduit of a blast furnace, can be cooled. The known injection lance comprises a central tube which serves for the supply of heating oil. The central tube is concentrically surrounded by a multi-wall outer tube in which oxygen is supplied; the oxygen serves for atomisation and combustion of the heating oil which issues from the central tube. For cooling purposes, the outer tube has a coolant duct which permits a circulation of coolant in the outer tube, by way of a feed connection and a discharge connection.
The object of the present invention is that of providing a method and an apparatus which provides improved cooling of the injection lance, which reduces the burn-back phenomenon.